Under anti-money laundering rules, banks are required to verify the ID of customers to make sure they are who they say they are.

This usually involves a 100-point ID check in a branch or an electronic verification using documents certified by a person qualified under statutory declarations rules, such as a justice of the peace. Any witnessing has to occur in front of the customer.

But according to claims made in an employee conduct file, seen by Fairfax Media, call centre staff have been told to witness and certify ID documents themselves using a stamp.The document claims staff were instructed to get documents stamped by a senior manager inside the call centre or stamp the documents themselves in the absence of customers.

NAB would not say how many planners had falsely witnessed the ID checks but said no customers had been negatively impacted.

"We became aware in mid-May of a small number of cases where client identification documentation may not have been correctly certified," NAB financial planning general manager Tim Steele said.

"We do not believe any customers will have been negatively impacted by what may have occurred, however we continue to work through this matter to understand exactly what has happened."

NAB would not confirm whether the Australian Securities and Investments Commission had been briefed on the issue.

Fairfax Media revealed last month that NAB financial planners had been falsely witnessing death beneficiary forms – legally binding documents that determine who gets a person's super when they die.

In response to that misconduct, NAB did not sack the planners, instead calling on them to "self-report" the behaviour and lose 25 per cent of their bonus.

Fairfax Media understands this latest issue surfaced as part of the bank's review into the false witnessing problems. NAB was heavily criticised in a banking inquiry in March for failing to discipline financial planners and their senior executives over previous scandals inside the wealth division.

The bank would not say what action it would take against planners in response to the latest misconduct. It said the stamps were not certifications in and of themselves, and were provided to staff to reduce the need for them to hand write their name and details.

"We take our obligations to all our customers very seriously, including our responsibilities to witness and certify all documentation accurately," Mr Steele said.

"If there has been a breach of process, appropriate action will be taken and the relevant regulatory bodies notified accordingly."